Planting of seeds directly on the ground in dry environment is very common in the world today. In many places the soil in which the seeds should be planted also lack nutrients, such as nitrogen (N), phosphorus (P) and potassium (K).
Several studies have shown that important aspects of seed germination and establishment are primarily the access to stable moisture and water conditions, more specifically capillary water.
Variations in microclimate, due to drying and wetting cycles during precipitation and sunshine have a negative influence on germination rates.
The method of seed coverage to increase the moisture conditions near the seed in order to help it germinate is a well-known technique for several hundreds of years.
It is also well known that small plants, plantlets, etc. need nutrients during growth, but a high concentration of nutrients during the initial germination stages can inhibit the germination, thereby the germination rate is reduced.
Rejuvenation of Forests
Compared to planting of plantlets, sowing is a cost-effective way to obtain a high number of stems per hectare. A high stem density provides the opportunities for high overall production/area and good wood quality. Direct seeding is therefore an effective and relatively inexpensive way to create a rejuvenation of forests, but there are still problems to be solved before direct sowing will be used in a larger scale.
One major problem with direct seeding is access to enough water in order for seeds to germinate. A substantial problem with direct seeding are therefore unstable and low germination results due to the high dependency on (unpredictable) precipitation and moisture conditions in the upper 2 cm soil layers. The availability of capillary water is however in most cases unlimited. The access to capillary water differs however due to the soil type, which together with other abiotic factors determines the evaporation rates. In sandy soils in the Nordic countries the evaporation near the surface is often so great that the upper part of the soil layer becomes too dry for seeds to swell and germinate. This is even more pronounced during hot summer days. For drier regions in the world, evaporation rates near the surface are often higher than in the boreal forest and the conditions for seed to germinate is even lower.
Moisture and accessible water have been studied in the north of Sweden during a period of 25 years. In a recent summary, it was verified that when a dry, sandy silty moraine is covered by a 1 to 2 cm of humus, the water potential is substantially higher and more stable than without this coverage. In fact the water potential in the study revealed that the moisture conditions were enough for the seeds to start swelling and germinate.
On average, only 10% of seeded pine seeds form plants after two years. To compensate for the low germination results, forest companies commonly supply seed in large amounts (40 000-60 000 seeds/ha) making the seed cost a substantial fraction of the whole regeneration costs. Another disadvantage is the fact that seeds from elite trees with long term higher growth are not feasible to use due to the high seed cost and limited seed supply. To be able to use elite tree seeds, new method and tools with a high probability for stable and high plant formation are needed.
The method of covering a seed to increase the moisture conditions near the seed in order to help it germinate is a well-known technique. It has however been uneconomical to perform in practise in the context of reforestation of forest areas due to the laboriousness of the task. In order to cost-efficiently carry out such a method a simplified device for seed coverage is necessary.
In most boreal forests there is also a lack of nutrients, such as nitrogen, potassium or phosphorus so there is a need to add a nutrient comprising at least one of these. The lack of nutrients especially nitrogen is regarded as the most limiting factor for tree growth in boreal forests.
In direct seeding there is need of a nutrient source, as the seeds are sown directly in the nutrient poor mineral soil. Especially, nitrogen is needed that is slowly released and remains in the surrounding soil of the newly sown seed for several years.
Thus, there is a need for a device which can absorb/trap capillary water and hold water, and simultaneously as it hold nutrients without reducing the germination rate.
Known Art
Different devices for handling and seeding of seeds are found on the market and in the patent literature. Such devices may contain container for the seed, water-absorbing materials and a part with nutrient. They can be formed as strips or bands, and be made of paper, starch or a decomposable material.
The US patent application US20120036733 present a felt material that can be used for seeding, which is composed of felt layer and a water absorbing containing layer.
The application GB2347836 describes a method of planting crops/trees/shrubs in arid areas without preparation to the land as in conventional practises in agriculture. The method involves the use of a biodegradable bag which may be rectangular, square or hexagonal in shape. The bag may contain a seed, root growth medium and fertilizer.
In KR100772992 a decomposable seed sealed sheet is provided to sprout and grow seeds in the original position by equally distributing and aligning the seeds at regular intervals according to the cultivation characteristic of the seeds. This sowing device is made of two layers of decomposable sheets made of starch or pulp and a seed layer in between these with a sprouting accelerator or a plant nutrient.
A similar paper tape is presented in CN201639950, which is intended for raising rice seeds into rice seedlings and making the rice seedlings bred suitable for rice planting machines.
A seed packing strip/plate with seeds having an adhesive layer used for fixing the seeds made by paper materials which are light and is easy to be dissolved is presented in CN101352119.
U.S. Pat. No. 2,648,165 describe a carrier for seeds comprising a permanently water-soluble adhesive material. The seed carrier may be formed from methyl ether of cellulose, or from either of the other synthetic resins or carbohydrates or their derivatives.
A plant sowing unit is presented in U.S. Pat. No. 5,802,763 utilizing a planting medium of growth material and a porosity increasing material and methods of preparing it. The porosity increasing material will keep water during the germination phase.
The U.S. Pat. No. 3,938,281 describes a germination and seedling assembly made of several peat bodies with a seed inside each unit. The peat bodies are placed in a plastic frame. The frame should be placed on the ground to absorb moisture from the ground to enhance the seeds to germinate. A problem with these frames is that the bottom of the frames are flat and will only partly be in contact with the soil, whereby a number of seed do not get access to water with a low germination rate as a result. Other problems have also been seen during use of these frames: birds learned to find worms under the frames and flipped them over, strong wind moved the plates, but the most severe problem was the low germination rate. The use of the device also turned out to be too complex and expensive.
In U.S. Pat. No. 3,733,745 a seedling promoting unit is presented, with a moister absorbing mass such as peat, the seed/seeds are placed on top of the peat and are covered with an evaporation protection supported by iron wires. The disadvantage with this is that the seed/seeds will not get in direct contact with capillary water from the ground. Furthermore, peat is hydrophobic after drying and thus have difficulties of reabsorbing moister once dried. A seed placed on top of a growth substrate is also exposed to sun and it is easily dried.
The invention WO 2008/044995 A1 describes a cylindrical seed planting unit, a planting arrangement for a seed planting unit, in the size of an ice hockey puck. The seed planting unit, the puck, is composed of a growth medium (peat) and one or several seeds placed at the top of the growth medium. A planting device is used to get the puck deep into the mineral soil in order to get it in contact with capillary water and swell several times, the seed will then germinate. One obvious disadvantage with this method is that the seed or seeds are placed on the top of the puck without protection from sun or seed predation. Another problem is as the puck swells the seeds are lifted upwards and are thereby continuously exposed for sun and repetitive wetting and drying cycles which reduces the germination rate. Several field trials have shown that this makes the formation of plants weather dependent.
Another invention, EP1253819, is related to a seed tape for a controlled germinating process and comprises arranged germinating units with a seed, which can be cut off one by one. This seed tape is made of two paper layers and optionally additives and a carrier in between. The paper in this invention should have a high wet strength.
The invention GB2365738 present a method of planting crops/trees/shrubs in arid areas without preparation to the land as in conventional practises in agriculture. The method involves the use of a biodegradable bag which may be rectangular, square or hexagonal in shape. The bag may contain a seed, root growth medium and fertilizer. Nothing is presented about how to attract moisture or water and keeping the nutrients close to the seed.
A manufacturing method of a seeding unit with an upper and lower film and seeds is presented in CN 1589600.
None of the above mentioned references present a way to combine large capacity of collecting water and binding of slow release nitrogen, which maintain or increase the germination rate.
Furthermore, nothing is taught about how the nutrients can be released during a long period of time after sowing the seeds.
In direct seeding other problems also exists. Wild animals or birds may eat the seeds. Rainwater can transport seeds that may have started to germinate to a non-favourable position where it could dry and die. If dry and windy, large coverage/lids may blow away. In most boreal forests there is also a lack of nutrients, such as nitrogen, potassium or phosphorus and there is a need to add a nutrient comprising at least one of these.
Thus there is a need for an easy applicable covering method and device which address the above-mentioned problems and needs. It is an objective of the present invention to provide a device and a method to address the above mentioned need.